The invention generally relates to offshore facilities for processing fluid minerals such as oil and gas reserves. More particularly the invention relates to a mobile, reusable jack-up type production facility designed to sequentially produce a plurality of smaller, so-called marginal, reservoirs economically. More particularly the invention relates to a jack-up structure which utilizes removable jacking towers and corresponding, reversible leg locks to allow jacking tower removal and/or installation while the platform is elevated.
In recent years there has been increased demand for hydrocarbons, yet the costs of recovering them from an offshore environment has increased such that the size of a profitably exploitable reservoir has become very large. Generally hydrocarbons from large reservoirs are processed by large fixed platforms which require an enormous capital investment to build, and to demolish, when production is complete. Smaller reservoirs are customarily produced by smaller fixed platforms, which are still relatively expensive to build, install and demolish when production is complete. In a few instances jack up structures which were originally designed for drilling operations have been permanently "converted", for service as a production platform. Those jack-up type structures have not solved the small-reservoir/high-capital-or-production dilemma in that they employ expensive jacking towers, motors and power supplies which are not designed to be conveniently installed and removed at will, thus these expensive components are not capable of servicing many structures economically.
There are increasing numbers of smaller reservoirs, with respectable quantities of hydrocarbons, which could be brought to market profitably if costs of recovery could be reduced.
Sumner U.S. Pat. No. 3,716,993, discloses a type of separately navigable drill ship which may be coupled with a variety of supporting structures through a spacing jack-and coupling structure. No means is provided to remove the operation components of the jacking devices while the drill ship is elevated.
Fischer U.S. Pat. No. 3,872,679, discloses a jack-up drill vessel which utilizes a combination of main legs (extending to the bottom of the water) and semi-submersible legs (which do not extend to the bottom of the water) to support or ballast the vessel as circumstances may require. No means is provided for removal of the jacking devices while the drill ship is elevated on location.
Giblon U.S. Pat. No. 3,927,535, discloses a large, deep water, jack-up type offshore drilling and production platform, which is stacked above two underwater platform support structures. Giblon states that after the upper platform is in an elevated position and the platform has been rigidly attached to each leg by welding-in a ring girder construction, the hydraulic jacks at each leg may be removed. However, no specific jacking mechanism or means for their removal, reinstallation or reuse is provided. No means is disclosed for lowering the platform once the legs have been welded to the upper platform.
Hellerman, et al U.S. Pat. No. 4,040,265, discloses a negatively buoyant truss type frame structure which may be used to receive and drydock a variety of separately navigable vessels. Hellerman, et al, states that after elevation of the vessel the platform mechanisms may be removed, but no specific jacking mechanisms, means for removal of the jacking mechanisms or means for supporting the platform during removal is provided.
Evans U.S. Pat. No. 4,227,831, discloses a jack-up type platform having an open keyway between two of the platform legs for accommodating conductor piping. The conductor piping is supported by underwater members attached between the legs lateral to the keyway. No means is provided for removal, reinstallation or reuse of the jacking mechanisms.
Evans U.S. Pat. No. 4,456,404, discloses a jack-up type drilling or production platform slidably supported by lateral wing walls, which walls are in turn supported by grounded legs. No means is provided for removal of the jacking towers while the platform is elevated.